On Wed, Mar 03 2021 at 6:57am -0500, Jeffle Xu <[email protected]> wrote:
> This method can be used to check if bio-based device supports IO polling > or not. For mq devices, checking for hw queue in polling mode is > adequate, while the sanity check shall be implementation specific for > bio-based devices. For example, dm device needs to check if all > underlying devices are capable of IO polling. > > Though bio-based device may have done the sanity check during the > device initialization phase, cacheing the result of this sanity check > (such as by cacheing in the queue_flags) may not work. Because for dm s/cacheing/caching/ > devices, users could change the state of the underlying devices through > '/sys/block/<dev>/io_poll', bypassing the dm device above. In this case, > the cached result of the very beginning sanity check could be > out-of-date. Thus the sanity check needs to be done every time 'io_poll' > is to be modified. > > Signed-off-by: Jeffle Xu <[email protected]> Ideally QUEUE_FLAG_POLL would be authoritative.. but I appreciate the problem you've described. Though I do wonder if this should be solved by bio-based's fops->poll() method clearing the request_queue's QUEUE_FLAG_POLL if it finds an underlying device doesn't have QUEUE_FLAG_POLL set. Though making bio-based's fops->poll() always need to validate the an underlying device does support polling is pretty unfortunate. Either way, queue_poll_store() will need to avoid blk-mq specific poll checking for bio-based devices. Mike > --- > block/blk-sysfs.c | 14 +++++++++++--- > include/linux/blkdev.h | 1 + > 2 files changed, 12 insertions(+), 3 deletions(-) > > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > index 0f4f0c8a7825..367c1d9a55c6 100644 > --- a/block/blk-sysfs.c > +++ b/block/blk-sysfs.c > @@ -426,9 +426,17 @@ static ssize_t queue_poll_store(struct request_queue *q, > const char *page, > unsigned long poll_on; > ssize_t ret; > > - if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL || > - !q->tag_set->map[HCTX_TYPE_POLL].nr_queues) > - return -EINVAL; > + if (queue_is_mq(q)) { > + if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL || > + !q->tag_set->map[HCTX_TYPE_POLL].nr_queues) > + return -EINVAL; > + } else { > + struct gendisk *disk = queue_to_disk(q); > + > + if (!disk->fops->poll_capable || > + !disk->fops->poll_capable(disk)) > + return -EINVAL; > + } > > ret = queue_var_store(&poll_on, page, count); > if (ret < 0) > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > index 9dc83c30e7bc..7df40792c032 100644 > --- a/include/linux/blkdev.h > +++ b/include/linux/blkdev.h > @@ -1867,6 +1867,7 @@ static inline void blk_ksm_unregister(struct > request_queue *q) { } > struct block_device_operations { > blk_qc_t (*submit_bio) (struct bio *bio); > int (*poll)(struct request_queue *q, blk_qc_t cookie); > + bool (*poll_capable)(struct gendisk *disk); > int (*open) (struct block_device *, fmode_t); > void (*release) (struct gendisk *, fmode_t); > int (*rw_page)(struct block_device *, sector_t, struct page *, unsigned > int); > -- > 2.27.0 > -- dm-devel mailing list [email protected] https://listman.redhat.com/mailman/listinfo/dm-devel
